High Temperat... S450EW Steel 陈继平.pdf

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DOI/s11595-022-2587-y
HighTemperaturePlasticDeformationBehaviorand
BrittleMechanismofS450EWSteel
CHENJiping1,HUXuewen2,QIANJianqing1
(,AnhuiUniversityofTechnology,Maanshan243032,China;,Maan-
shan243000,China)
Abstract:High-temperaturetensiletestswereconductedforhighcorrosionresistantweatheringsteel
,dislocationsandprecipitateswereinvestigatedbyfleld
-temperatureplastic

thattheductilitytroughsappearat700-850℃and650-900℃whenthestrainratesare3×10-×10-2
s-1,,
hotductilityisbestwhenthecoolingrateis5℃/sbeforedeformationat750℃andtheareareductionrate
%.Finesecondphaseparticlesandinclusionsprecipitatedbeforeandduringdeformationprovide

tocausestressconcentrationwhichresultsinmicrocracksormicrovoidsbetweengrainsduringdeformation


inducedproeutectoidferritefilmsdistributealongtheaustenitegrainboundarieshinderthedynamic
.
Keywords:corrosionresistantsteel;hotductility;dynamicrecrystallization;DIFT;brittlemechanism
1Introductioningpossibilityandcauseofcracksduringhotrolling[1-5].
MehtonenSVetal[6]studieddynamicrecov-
AsanupgradedproductofweatheringsteelforerymechanismofTi-Nbstabilized21%Crferritic
railwayfreightcars,highcorrosionresistantweatheringstainlesssteelduringhotcompressionatdeformation
steelS450EWhasstrongercorrosionresistancethantemperatureof950-1050℃-10
previousgenerations,avoidspaintingpollutionands-[7]consideredthatcoarseaustenite

ThehotductilityofS450EWsteelisdirectlyrelatedreflnedbydynamicrecrystallizationathigherdeforma-
tocomposition,-1200℃andlowerstrainrate
-5s-

duringcontinuouscastingandhotrollingprocess,[8-10]studiedthecorrosionresistant
necessarytostudythehotductilityofS450EWsteelpropertiesandcorrosionresistantmechanismofMn-
andprovideimportantreferenceandtheoreticalbasisCuPweatheringsteelinsimulatedindustrialandmarine
forformulatingappropriatesecondarycoolingrules,[11]studiedthe
dynamicsoftreductionvaluesandstraighteningtem-dynamicrecrystallizationbehaviorofhightemperature
peratureofslabsduringcontinuouscastingandanalyz-deformedausteniteinCu-P-Cr-Ni-Moweatheringsteel
undertheconditionofconstantstrainrateanddefor-
©WuhanUniversityofTechnologyandSpringer-,
Germany,PartofSpringerNature2022thereflnementmechanismofmicrostructuretransforms
(Received:,2021;Accepted:,2021)fromausteniterecrystallizationreflnementtoferritere-
陈继平
CHENJiping():.;PhD;E-mail:[12]studied
******@
FundedbytheNationalNaturalScienceFoundationofChinatheweldedjointofS450EWnewweatheringsteelwith
()highcorrosionresistancebytensile,impact,bending,
JournalofWuhanUniversityofTechnology-

foundthatthefatiguestrengthandcorrosionresistance
ofthejointweregreatlyimprovedcomparedwiththe
traditionalweatheringsteel.
Insummary,domesticandforeignscholarsare
mainlyconcentratedinthestudyofcorrosionresistant
propertiesandcorrosionmechanismofthetraditional
weatheringsteelandnewhighstrengthcorrosionre-
,

steel
-
tantweatheringsteelS450EW,literaturereportsare20,and50℃/swereusedtoreducethedeformation

temperaturetoughness,itshightemperatureplastictemperaturetensiletestwere600,650,700,725,750,
deformationbehaviorresearchhasnotbeencarriedout775,800,850,900,950,1000,1050,1100,1150,
,thehightemperature1200,and1250℃.Thespecimenswereimmediate-
plasticdeformationbehavioranddynamicrecrystal-lycooledbyairtomaintainthefracturemorphology


deformationcharacteristics,flowstresscurves,
temperaturebrittlenessmechanismanddynamicrecrys-weremeasuredbyaverniercaliperwithanaccuracy
tallizationwereanalyzed,-



werecarriedoutinaccordancewithGB/T4338-2006

cut,groundedandpolished,thenimmersedin4%nitric
Thehotductilitycurvesofhighcorrosionresis-
tantweatheringsteelS450EWwereobtainedbyhighNovaNanoSEM430fleldemissionscanningelectron
-
,andhightemperature
plasticdeformationbehaviorandbrittlemechanism
Table1ChemicalcompositionofS450EWsteel/wt%

CSiMnPSCrCuAl
transmissionelectronmicroscopyexaminationwere

punchedoutfrom50μmthickslices,andelectropo-
Thehightemperaturetensiletestschemeislistedlishedinasolutionof5%perchloricacidinethanol
asfollows:theslabswerecutintocylindricaltensileat-30℃inaMTP-1ATwinJetElectropolisher,set
specimenswithexternalthreadsatbothendsof10atavoltageof30--
mm×,sizeanddistributionoftheprecipitatesaswellas
℃atarateof10℃/sandheldfor3minonaGlee-dislocationsconfigurationwereobservedusingJEM-
ble-3500thermalsimulationtestingmachineatalow2000FXtransmissionelectronmicroscopyoperatedat
.
cooledtothedeformationtemperatureatthecooling
ratesof1and5℃/,thespec-3Resultsanddiscussion
imenswerestretcheduntilfractureatthestrainratesof
3×10-3,×10-2,and5s-1(strainrate3×10-3s-
equivalenttothestrainrateduringcontinuouscastingThehotductilitycurvesofS450EWsteelatstrain
-3-2-1
straightening,andstrainrate5s-1wasusedtosimulateratesof3×10,×10,.
thehotrolling).Inaddition,thecoolingratesof1,5,ItcanbeseenthattheductilitytroughofS450EWsteel
:HighTemperaturePlasticDeformationBehaviorandBrittle...

appearsat700-850℃whenthestrainrateis3×10-
s--TheSEMmorphologiesoffracturemicrostruc-
rowandthebottomtemperatureofductilitytroughisturesatstrainrateof3×10-3s-1,deformationtem-
750℃.900-1150℃isthebestplasticdeformationperatureof750℃andcoolingratesof1and5℃/s
(a)that
-
ductilityisstillhighbetween1150and1250℃,andtenitegrainboundariesinthefracturemicrostructures
theareareductionrateismorethan78%.Theduc--
tilitytroughofS450EWsteelappearsat650-900℃tion,indicatingthattheferritefllmsareformedduring
×10-2s-
isslightlywiderthanthatofstrainrateof3×10-
s-1andthebottomtemperatureoftheductilitytroughistosay,theferritefilmsareformedthroughDIFT
is725℃.900-1100℃isthebestplasticdeformation(deformationinducedferritetransformation).From
(c)-4(f),itcanbeseenthatpartialCrsecond

ofS450EWsteelishighinthewholetemperaturerangethedeformationinducedeflecthinderdynamicrecrys-
andtheareareductionratesareabove61%.Withthetallizationprocessandpromoteformationandpropa-
increaseofstrainratesfrom3×10-3to5s-1,

lowertemperatureside,whichvariesfrom750℃.
thebeginningof3×10-3s-1to650℃at5s--Ca,Al,Cu,S,Mn,Oandothercompositeinclusions
creaseofstrainrateimprovesthehotductilityofbrittlewithparticlesizeofabout1-2μmexistinthecracks
(a)-4(b)that
1,5,20,and50℃/sbeforedeformationat750℃iswiththeincreaseofcoolingratefrom1to5℃/s,the
,thephasetransforma-
to50℃/s,thehotductilityisthebestat5℃/sandthetiontemperaturedecreasesandtheamountofferrite
%.
isuniformlyformedintheausteniteandthegrain

-
%%andthe
hotductilitybecomesbetter.
×10-2s-1andthede-
formationtemperatureis725℃,theSEMimageis


,O,andSioxideswithsizeabout4-
ratesbeforedeformationat750℃6μm.
JournalofWuhanUniversityofTechnology-
(a)SEMimageoffractureatcoolingrateof1℃/s;(b)SEMimageoffractureatcoolingrateof5℃/s;(c)-(d)SEMimagesofparticles
atthefracture;(e)-(h)Energyspectraofparticlesa,b,canddatstrainrateof3×10-3s-1anddeformationtemperatureof750℃

ductilityisgreatlyimproved.

Akben’sresearchshowsthatdynamicrecrystalli-
zationanddynamicprecipitationcanoccursimultane-
ously,whichinfluenceandrestricteachotheratlower
strainratesdeformation[13].Ontheonehand,dynamic
precipitationofsecondphaseparticlespreventsmi-
grationofgrainboundaries,subgrainboundariesand
dislocationsanddelaysthedynamicrecrystallization.
Ontheotherhand,dynamicrecrystallizationprocess
willeliminateorreducevariousdefectssuchasgrain
boundaries,subgrainboundariesanddislocations,re-
(a)SEMmorphologyoffracture;(b)SEMmorphologyof
particlesatthefracture;(c)Energyspectrumofparticleaatducethenucleationpositionsofprecipitatesandinhibit
×10-2s-1anddeformationtemperatureofthedynamicp